Taxpayer-controlled Royal Bank of Scotland plans to cut an extra 300 jobs at its investment bank, according to figures released today.RBS now aims to cut 3,800 roles at its investment banking arm by the end of 2013, 300 more than previously anticipated.The lion's share of those jobs, 3,000, will be gone by the end of this year.The numbers were revealed in slides that John Hourican, RBS's head of markets and international banking business, will use at an investor presentation on Monday.There he will explain that the bank's plans to exit its loss-making cash equities, corporate broking, equity capital markets and mergers and acquisitions businesses are going to plan.RBS is 82%-owned by the British taxpayer after the government had to step in with a £45.5bn rescue package during the 2008 credit crisis.